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Introduction
Agriculture, worldwide, is a fundamental activity for the subsistence of human population. Several factors have deteriorated their resources and caused the growing difficulty to renew them. The soil as the basis of resources and production is framed in a complex, heterogeneous and fragile environment, which shows high susceptibility to erosion and low natural fertility, with negative effects on crop production, labor productivity and the feasibility of establishing sustainable production systems. The recovery and maintenance of soil fertility on a sustainable basis is a very important factor in the development of grasses production worldwide (Rueda-Puente et al.2015).
Grasses are an appropriate source of nutrients for cattle, mainly in countries with a tropical climate, due to the high number of species that can be used, the possibility of cultivating them all year, the ruminant's ability to use forages, no competition with food for humans and an economic source (Patiño et al. 2018). However, the lack of forage species of good quality, adapted to the prevailing environmental conditions in the different livestock areas is one of the problems that most limit the development of livestock (Uvidia et al. 2015).
To mitigate this situation, great efforts have been made in the introduction of new species and varieties of higher yield and quality, such as Megathyrsus maximus, in the Ecuadorian Amazon. However, its growth, productivity and quality are unknown as the age of the plant increases. Hence, the objective of this study was to evaluate the quality of three Megathyrsus maximus cultivars in the Empalme area, Ecuador at different regrowth ages.
Materials and Methods
Location. This research was carried out at the Orlando Varela farm, located at kilometer one of the El Empalme - Balzar road, left margin, democracy sector, El Empalme canton, Guayas province, Ecuador. It is located between the geographical coordinates 01° 06' of south latitude and 79° 29 of west longitude at a height of 73 m o.s.l. In the period between July-September (dry season) 2015.
Agrometeorological conditions. The climate of the territory is classified as humid subtropical, with average rainfalls of 2229.60 mm/year. The average temperature is 25.80 °C; relative humidity 86 %, Inceptisol soil (Soil Survey Staff 2003) and its chemical composition is in table 1.
Treatment and experimental design. A randomized block design with factorial arrangement (3x3) was used: three Megathyrsus maximus cultivars (Common, Tanzania and Tobiata) and three regrowth ages (21, 42 and 63 days) and five replications.
Procedure. The experimental plots (5x5 = 25m2) were sowing in February 2015 of Megathyrsus maximus cultivars Common, Tanzania and Tobiata at a distance of 50 cm between rows and 20 cm between plants. The plants had a period of establishment until July, where the uniformity cut was made. From there, samplings at 21, 42 and 63 days of regrowth were made, eliminating 50 cm of border effect and cutting all the material from the harvestable area at 10 cm above soil level. The biomass production, yield of total dry matter, leaves and stems, number of leaves and stems (by bunch), as well as the length and width of leaves, and the leaf-stem relation were evaluated. Then two kilograms were taken for each of the treatments and for replication for further analysis in the laboratory.
Only irrigation was used to facilitate germination and establishment, and no fertilization or chemical treatment was used to eliminate weeds. At the beginning of the experiment, the population of the varieties in the plots was 99 %.
Determination of chemical composition. The DM, CP, ash, OM, P, Ca were determined according to AOAC (2000); NDF, ADF, ADL, cellulose (Cel), hemicellulose (Hcel) and cellular content (CC) according to Goering and Van Soest (1970); the digestibility of dry matter was quantified by Aumont et al. (1995) and the metabolizable energy and net lactation energy were established according to Cáceres and González (2000). All analyzes were performed in duplicate and by replication.
Statistical analysis and calculations. Analysis of variance was performed according to the experimental design and mean values were compared using Duncan’s (1955) multiple range test. For the normal distribution of the data the Kolmogorov-Smirnov (Massey 1951) test was used and for the variances the Bartlett (1937) test.
Results
For all the studied indicators, there was interaction (P <0.0001) variety x regrowth age. The highest yield of DM (4.18 t/ha) was obtained with the Tanzania variety at 63 days of regrowth and all varieties increased this indicator with their maturity. Similar pattern of response was showed in the yield of biomass, leaves and stems (table 2)
When analyzing the morphological indicators (table 3) the best results in the height, number of leaves, number of stems, leaves length and leaves width were obtained in Tanzania variety at 63 days of regrowth with 158 cm; 667.45; 112.58; 0.76 m and 0.05 m, respectively.
Table 2 Components of the yield of three Megathyrsus maximus varieties
abcdefg Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
Table 3 Morphological indicators of three Megathyrsus maximus varieties
abcdefghi Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
The highest value of CP and cellular content (CC) was recorded after 21 days of regrowth in Tanzania variety (12.56 % and 64.40 %, respectively), while the highest values for the fibrous components (NDF, ADF, ADL and Cel) were obtained in the Common variety at 63 days of regrowth (66.50, 33.49, 4.41 and 29.08 %, respectively). The Tobiata variety excelled in the hemicellulose content (33.56 %) at 63 days of regrowth (table 4).
Table 4 Protein content and fibrous fractionation of three Megathyrsus maximus varieties
abcdefgh Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
Minerals and organic matter (table 5) showed significant interaction variety x regrowth age. The highest percentages of ashes (14.26) were obtained in Tobiata variety at 63 days; those of Ca (0.58 %) corresponded to Tanzania with 63 days of regrowth and those of P (0.26 %) and OM (90.85 %) were registered in the Common variety at 63 and 21 days of regrowth, respectively.
Table 5 Tenors of minerals and organic matter of three Megathyrsus maximus varieties
abcdefghi Values with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
There was significant interaction variety x age of regrowth for leaf/stem relation, NDF/N and ADF/N, as well as for DMD, OMD, ME and FNE. The highest values were obtained in the Common variety and were 12.50 (21 days), 12.49 (63 days), 6.29 (63 days), 54.82 % (21 days), 50.68 % (21 days), 7.28MJ/ kg (21 days) and 4.07MJ/ kg (21 days), respectively (table 6).
Table 6 Some quality indicators of the three Megathyrsus maximus varieties
abcdefghiValues with different letters differ at P<0.05 (Duncan 1955)
1SE, standard error of the interaction variety x age
Discussion
Verdecía et al. (2015) when studying two varieties of Megathyrsus (Tanzania and Mombasa), with 75 days of regrowth, in the eastern region of Cuba found total yields, of leaves and stems of 9; 5 and 4 tDM/ ha, respectively. These values are similar to those found in this research. On the other hand, Uvidia et al. (2015) when studying Cenchrus purpureus vc. Maralfalfa reported similar performance until 90 d of age.
The eastern region of Cuba is characterized by high temperatures, rainfalls no more than 1000 mm, and eroded and degraded soils, while in the area where this research was carried out, temperatures are lower and rainfalls are twice as high. This indicates the ability of these varieties to adapt and produce under different conditions.
On the other hand, it is proposed that any variation that exists in the physiological processes is a response to the thermal regime, precipitation and its distribution and directly influence on the production of dry matter and its components, although it is necessary not to ignore other aspects that are included in the management of grasses such as regrowth age, cut frequency, cut height and fertilization, among other aspects. Different studies carried out in Cuba (Verdecia et al. 2015, Herrera et al. 2017 and Ramírez et al. 2017a) showed the influence of climatic elements on the yield and quality of several grasses species, including secondary metabolites. In these studies, the marked positive influence of the rains and the temperatures on the yields and their components was demonstrated, but the negative effect produced by the low temperatures and the water deficit in the mentioned indicators was clearly established.
Ramírez-Pedroso et al. (2017b) and Rosales et al. (2017) when carrying out studies in the Likoni cultivar of application of mycorrhizal fungi strains found yields of 2.53 tDM and increments of 1.45 tDM when using this type of fertilizer. On the other hand, Muñoz et al. (2017) when evaluating this variety in association with temporary legumes (Canavalia ensiformis and Lablab purpureus) during the dry period achieved 26.36 t GM of biomass in monocultures and up to 39.38 in association with Canavalia.
The increase in the morphological indicators, plant height, number of leaves and stems per bunch, as well as the length and width of leaves is determined by the interaction variety x regrowth age. The highest proportion of leaves during the first regrowth ages can be due to the appearance of tillers and the need of the plant to create the necessary substances for its development (Álvarez-Perdomo et al. 2016). However, it is known that from a certain regrowth age these indicators can decrease and is associated with the increase in the stems and their thickness, among other aspects (Vargas et al. 2014), but this did not happen in this research since advanced regrowth ages were not studied.
Other studies (Fortes et al.2014) reported that varieties of Megathyrsus genus during the dry season, in response to low temperatures, to the decrease light hours and rainfalls, tend to develop less the stem and increase the leaves proportion to capture the greatest amount of solar radiation to perform photosynthesis (Fortes et al. 2016). This could contribute to explain the performance of the morphological indicators studied.
Vargas et al. (2014) showed the Absolute Growth Rate of Megathyrsus maximus cv. Mombaza under Amazonian ecosystems conditions and noted that there is accelerated growth until 40 days of regrowth at a rate of 2.5 cm per day, from which grows more discreetly and attributed to the physiological adaptations of plants, as a result of climatic factors prevailing in the region, which allow the development and perpetuation of this species. These aspects coincide with what was stated in this research.
For the chemical composition there was interaction variety x regrowth age. However, in all varieties the DM, NDF, ADF, ADL, Cel and Hcel were increased, while CP and CC decreased with the regrowth age. This process is due to the fact that depending on the type of tissue, as the cell of the plant matures, the cell wall widens and commonly produces a secondary wall of different composition, so chemical and anatomical changes occur that affect the digestibility. This was related to that in younger ages there is higher leaf succulence and more young stems (Bayoli et al. 2008).
In this regard, Moreno (2004) and Fortes et al. (2016) stated that when comparing the nutritional value of forages, the variability is small between cultivars and varieties from the same genus, while the greater differences are appreciated when comparing forage grass genera. However, the values of the components of the cell wall, CP and CC are within the range reported by the literature, but it is to be noted the low values of lignin that these three varieties presented.
Regarding the content of minerals and organic matter despite the interaction found, there was little variability among the varieties attributable according to Verdecia (2015) to the effect of climate factors specifically rainfalls and temperatures, which lead to the minerals needed to the growth of plants are in the soil dissolution and the roots have relative ease for their absorption. However, Patiño et al. (2018) found that ash tends to decay with increasing age, because plants require different amounts of minerals depending on their phenological state.
In relation to the quality indicators, the interaction found is indicative, not only for these indicators, that the regrowth age and the varieties have to be considered as a system and not as independent factors, since they will be developed under certain conditions of climate, soil and management. The leaf/stem ratio favorable to the amount of leaf and to the little development of the stem was encouraging. However, that low stem content could be a negative element, since this organ is a reservoir of reserve substances necessary for rapid regrowth after cutting or grazing. This is increased by the unfavorable ADF/N and NDF/N ratios which are determined by the low nitrogen content and high fiber value.
Gaviria et al. (2015a b) have pointed out the importance of the constitutive substances of the plant for their growth and development, especially when silvopastoral systems are used where the grass plays a fundamental role and this was evidenced in the Leucaena-Megathyrsus system. In addition, these authors showed the importance of the grass tillering, as well as the role played by the thickness and development of the stem in some quality indica- tors.
Other studies (Álvarez-Perdomo et al. 2016) report that varieties of the Megathyrsus genus in response to low temperatures, to the decrease of light hours and rainfall during the dry season, tend to develop less the stem and increase the proportion of leaves to capture as much solar radiation as possible to perform photosynthesis.
In relation to digestibilities and energy content, it can be considered that they are within the range of values reported by the literature, when considering that they were obtained under conditions of high precipitation and in soil that is not very favorable for the cultivation of these species. However, the relative lower values of DMD, OMD and energy contributions, with the advance of maturity can be attributed to the increase of stems, which are related to the increase in the content of the cell wall components, which promote greater formation of covalent bonds of lignin with the structural carbohydrates of the cell wall and limit their digestion, and therefore the energy contribution (Villareal et al. 2014).
The results of this research showed variability regarding the varieties in the studied indicators, since similar response patterns were obtained, but with different absolute values with the best general performance for Tanzania. However, it was showed that as the maturity of the plant advanced, there was a decrease in its nutritional quality, among other aspects, by the decrease in leaf-stem ratio, digestibilities and energy, as well as increases in the relations NDF/N, ADF/N, aspects to take into account in the management of these plants as food for cattle, with the aim of improving their use efficiency. In addition, the use of the Common and Tobiata varieties should not be rejected. It is recommended to carry out future researches on the management of these varieties and their influence on the production of milk and meat.
